Field of the Invention
The present invention relates to a CVT transmission having a start-up element, a variator, and having a direct-shift stage for switching between the first operating range (low) and a second operating range (high). In addition, the present invention relates to a method for operating such a CVT transmission.
Description of the Related Art
The term CVT refers to a stepless transmission; the letters CVT stand for continuously variable transmission. To increase the transmission ratio range of a stepless transmission—its gear ratio spread-it is known from European published unexamined application EP 2 275 709 A1 to position a planetary gear set after the stepless transmission. The controllable planetary gear set enables two-range shifting and shifting into reverse. In addition, it is known from German published application DE 102 61 990 A1 to provide a multi-range CVT with fixed engageable gears, for example for moving off or for top speed; however, when these fixed transmission ratios are in operation the variator is uncoupled. Consequently, there is only one stepless range; stepless operation is not possible in all driving ranges.
An object of the present invention is to simplify the operation of a CVT transmission having a start-up element, a variator, and having a direct-shift stage for switching between a first operating range (low) and a second operating range (high).